The Debian nvidia-glx package (at least the one in Etch) stores the original Mesa libglx as /usr/lib/nvidia/libglx.so.xlibmesa, which you may want to symlink as /usr/lib/xorg/modules/extensions/libglx.so to avoid the undefined symbol error.

Running git commands (such as git clone and git checkout) may yield the following message:

If you are looking for git, Linus Torvald's content tracker, install
the cogito and git-core packages and see README.Debian and git(7).
This transition script will be removed in the debian stable
release after etch.
If you wish to complete the transition early, install git-core
and use (as root):
update-alternatives --config git
Press RETURN to run gitfm

If this is the case, run update-alternatives --config git as root, and select the /usr/bin/git-scm alternative (option 1 in the following example):